1. Field of the Invention
The present invention relates generally to the field of industrial power generation and circulating fluidized bed (CFB) reactors and combustors having impact-type particle separators, and, in particular to a new and useful impact-type particle separator for a CFB.
2. Description of the Related Art
In CFB reactors or combustors, reacting and non-reacting solids are entrained within a reactor enclosure by an upward gas flow which carries the solids to an exit at an upper portion of the reactor enclosure. There, the solids are typically collected by an impact type primary particle separator, and returned to a bottom portion of the reactor enclosure either directly or through one or more conduits. The impact-type primary particle separator at the reactor enclosure exit typically collects from 90% to 97% of the circulating solids. If required by the process, an additional solids collector may be installed downstream of the impact-type primary particle separator to collect additional solids for eventual return to the reactor enclosure.
As disclosed in U.S. Pat. No. 5,343,830, the use of impact-type particle separators in CFB reactors or combustors is well known. To the extent necessary to describe the general operation of CFB reactors and combustors, the reader is referred to U.S. Pat. No. 5,343,830, the text of which is hereby incorporated by reference as though fully set forth herein. In one of the earliest CFB designs, an external, impact-type primary particle separator having a plurality of impingement members arranged in staggered rows was used in combination with a non-mechanical L-valve and a secondary (multiclone) particle separator. The rows of staggered impingement members discharged all of their collected solids into a storage hopper located underneath them, and these collected solids were returned to the bottom portion of the reactor enclosure via the L-valve.
Later CFB designs employed additional rows of staggered impingement members which were positioned upstream (with respect to a direction of flue gas and solids flow through the apparatus) of the impingement members associated with the storage hopper and its L-valve. As disclosed in U.S. Pat. No. 4,992,085, the text of which is hereby incorporated by reference as though fully set forth herein, a plurality of such impingement members are located within an upper portion of the reactor enclosure, arranged in at least two staggered rows. The impingement members hang and extend vertically across a width of the reactor exit, with collected solids falling unobstructed and unchanneled underneath these collecting impingement members along a rear enclosure wall of the CFB reactor or combustor. An important element of these xe2x80x9cin-furnacexe2x80x9d collecting impingement members, or xe2x80x9cin-furnace U-beamsxe2x80x9d as they are generally referred to, is a baffle plate near a lower end of these impingement members which enhances their collection efficiency.
As disclosed in the aforementioned U.S. Pat. No. 5,343,830, CFB reactors or combustors are known wherein the two or more rows of impingement members located within the furnace or reactor enclosure are followed by a second array of staggered impingement members which further separate particles from the gas stream, and return them via cavity means and particle return means without external and internal recycle conduits.
U.S. Pat. No. 6,095,095 teaches a further improvement in impact-type solids separators for a CFB which is a simpler and lower cost impact-type primary particle separator. Instead of providing a cavity means or hopper with discharge openings underneath the collector elements making up the impact-type primary particle separator, the separator of U.S. Pat. No. 6,095,095 has a simple floor for internal return of all primary collected solids to a bottom portion of the reactor or combustor for subsequent recirculation.
U.S. Pat. No. 6,095,095 does not address the mechanical aspects of the individual separator elements, however, including relative thermal expansion between the elements (or U-beams) and the enclosure walls. As noted above, a hopper is not used in the separator of U.S. Pat. No. 6,095,095.
It is often desirable to utilize collection elements like U-beams made of stainless steel and hung from the roof of the CFB reactor while operating in a floored impact collector mode. However, when a solid floor is located beneath the collector elements, the U-beams may expand onto a pile of solids as a result of thermal expansion of the U-beam metals. When the collection elements touch the solids piles, a high compressive force is exerted on the long dimension of the U-beams. Thus, because of the large thermal expansion in the length of the U-beams which can be expected with stainless steel U-beams and the need to avoid placing large compressive forces on the U-beams, a gap must be available between the lower ends of the U-beams and enclosure floor so that the collection elements can freely expand.
It is an object of the present invention to provide an impact-type separator for a CFB which accounts for thermal expansion of the separator elements.
A further object of the invention is to provide an arrangement of collection elements having gaps for free thermal expansion of the elements within the enclosure in a floored collection element environment.
Accordingly, a collection element arrangement is provided having attachments near their lowermost ends which simulate a continuous sloping surface, or floor. The sleeve attachments"" upper surfaces, forming the floor, permit collected solids to flow down the sloping surface back into the furnace or reactor chamber. The sleeve attachments are fitted around each element. The outer wall of each attachment is positioned to leave a small gap between the adjacent sleeve and/or CFB enclosure walls. The upper surface of the sleeve attachments block off the lower ends of the collection elements as well. The attachments are integrally connected with the collection elements, so that they expand together through increasing temperatures in the CFB during operation startup.
In an alternative embodiment, the CFB may include a staggered array of heat exchange tubes for solids collected by the collection elements to pass through prior to returning to the reactor chamber.